Liquid development of latent electrostatic images

ABSTRACT

A LATENT ELECTROSTATIC IMAGE ON A SURFACE OF A CARRIER MOVING ALONG A DEVELOPING PATH IS DEVELOPED INTO A VISIBLE IMAGE BY BRINGING THE IMAGE-BEARING SURFACE INTO CONTACT WITH DEVELOPING LIQUID AND TRANSPORTING IT OVER AN ELONGATED DISTANCE IN SUBSTANTIALLY CONSTANT SPACED RELATION TO AN ELECTRICALLY CONDUCTIVE SURFACE OF AN IMAGE INTENSIFIER. THE DEVELOPING LIQUID IS APPLIED TO THE SURFACE OF THE IMAGE INTENSIFIER WHICH MOVES ALONG THE DEVELOPING PATH, AND THE IMAGE-BEARING CARRIER IS TRANSPORTED PAST THE MOVING SURFACE BY AN ENDLESS TRANSPORT BELT MOVING AT SUBSTANTIALLY THE SAME SPEED AS THE IMAGE-BEARING CARRIER SO AS TO AVOID RELATIVE MOVEMENT THEREBETWEEN AND HENCE ELIMINATE SCUFF MARKS ON THE BACK OF THE CARRIER. AFTER MOVEMENT PAST THE IMAGE INTENSIFIER, THE IMAGE-BEARING CARRIER IS PASSED BETWEEN A PAIR OF ROTATABLY DRIVEN SQUEEGEE ROLLERS WHICH REMOVE EXCESS DEVELOPING LIQUID FROM THE CARRIER AND PRESS THE VISIBLE PARTICLES INTO THE SURFACE THEREOF. THE SQUEEGEE ROLLERS ARE WIPED BY A POROUS WIPER WHICH EXTENDS INTO CONTACT WITH THE MOVING SURFACE OF THE IMAGE INTENSIFIER SO AS TO BECOME SOAKED WITH DEVELOPING LIQUID ON THE MOVING SURFACE OF THE IMAGE INTENSIFIER.

Aug. 29, 1972 G. J. MILLER 3,687,708

LIQUID DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES Filed May 21, 1969 4 Sheets-sheaf. 1-

INVENTOR GEORGE J. MlLLER.

I ATTORNEYS Aug. 29, 1972 G. J. MILLER 3,587,703

LIQUID DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES Filed May 21, 1969 4 Sheets-Sheet 2 INVENTOR GEORGE J. MkLLER.

Aug. 29, 1972 G. J. MILLER 3,537,703

LIQUID DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES I Filed May 21, 1969 4 Sheets-Sheet s -v111 11 I I I l I! 11 11 I! 1 1111 INVENTOR GEORGE J. MILLER.

Aug. 29, 1972 G. J. MILLER 3,537,703

LIQUID DEVELOPMENT OF LATENT ELECTROSTATIC IMAGES Filed May 21, 1969 4 Sheets-Sheet 4 INVENTOR GEORGE. J. MlLLEE.

1245A f/[w LL ATTORNEYS United States Patent US. Cl. 117-37 LE 16 Claims ABSTRACT OF THE DISCLOSURE A latent electrostatic image on a surface of a carrier moving along a developing path is developed into a visible image by bringing the image-bearing surface into contact with developing liquid and transporting it over an elongated distance in substantially constant spaced relation to an electrically conductive surface of an image intensifier. The developing liquid is applied to the surface of the image intensifier which moves along the developing path, and the image-bearing carrier is transported past the movingsurface by an endless transport belt moving at substantially the same speed as the image-bearing carrier so as to avoid relative movement therebetween and hence eliminate scuff marks on the back of the carrier. After movement past the image intensifier, the image-bearing carrier is passed between a pair of rotatabl'y driven squeegee rollers which remove excess developing liquid from the carrier and press the visible particles into the surface thereof. The squeegee rollers are wiped by a porous wiper which extends into contact with the moving surface of the image intensifier so as to become soaked with developing liquid on the moving surface of the image intensifier.

This invention relates to electrostatic photocopying, and more particularly to the development of a latent electrostatic image on a surface of a carrier into a uniform visible image by a developing liquid.

In electrostatic photocopying, an original document is copied by first producing a latent electrostatic image of the original on'asheet of copy paper, or other suitable carrier, and-then developing the latent image into a visible image; To form the latent electrostatic image, a uniform electrostatic charge is imparted to a suitable carrier, for examplea sheetof copy paper, which has a photoconductive surface, and an image of the original to be copied is projected onto the photoconductive surface of the carrier. As the photoconductive surface is exposed to the image of the original, the uniform electrostatic charge is selectively discharged according to the intensity of the projected image, which varies proportionally according to the light and dark areas of the original. After a period of time sufficient to enable the light areas of the original to almost completely discharge the electrostatic charge on the corresponding areas of the copy, a latent electrostatic image of the original is formed on the surface of the carrier.

To develop the latent electrostatic image into a visible image, the image-bearing surface of the carrier is brought into contact with a developing liquid having visible particles which are electrically attractable to the areas of the photoconductive surface having a latent electrostatic charge. During contact with the developing liquid, the visible particles are deposited on the image-bearing areas of the paper so as to develop the latent electrostatic image into a visible image. Subsequently, the image-bearing carrier is removed fromcontact with the developing liquid and passed between a pair of squeegee rollers which remove excess developing liquid from the carrier and press the visible particles into the surface thereof to provide a permanent copy of the original document.

3,687,708 Patented Aug. 29, 1972 In the development of a latent electrostatic image, it is desirable that the visible particles be deposited uniformly on the portions of the image having the same uniform electrostatic charge. However, oftentimes in the development of an image having an area of uniform charge, the visible particles are deposited more densely along the fringe of the area as contrasted with the central portions thereof, and this phenomenon is referred to as fringe development. The problem of fringe development is believed to center around the fact that the latent electrostatic image produces an electrostatic field having lines of force, and fringe development is believed to result from a distortion in the electrostatic field, wherein the lines of force are concentrated along the fringe of the image. Accordingly, the electrostatic field is more intense along the fringe of the image, and this causes the visible particles to be attracted, and hence deposited more densely along the fringe of the image.

Another problem encountered in the development of a latent electrostatic image is that undesirable scuff marks are sometimes placed on a surface of an image-bearing carrier as it moves along the developing path. The scuff marks result from the surface of the carrier scraping against undesirable accumulations of the visible particles of the developing liquid which tend to build-up on stationary surfaces along the developing path. Such undesirable accumulations of visible particles are even more likely to occur where there are ridges or other protrusions formed in the stationary surfaces.

In addition, the visible developer particles tend to adhere to the surface of the squeegee roller which presses against the image-bearing surface of the carrier. The accumulation of developer particles on the squeegee roller is particularly undesirable, because it tends to cause over printing on the surface of the carrier. In the past, the squeegee rollers have been wiped with a porous material to remove any accumulation of developer particles which could undesirably affect the imagebearing carrier. However oftentimes the wipers become dry when the photocopying machine has been inoperative for an extended period of time, and when the vmachine'is subsequently operated the dry. squeegee wiper produces squeaking noises and causes streaks on the image-bearing surface of the carrier. Such a condition persists until sufficient copies have past through the squeegee rollers to enable the porous wiper to become dampened wtih developing liquid.

Accordingly, an object of the present invention is to provide uniform development of a latent electrostatic image by maintaining the image-bearing surface of the carrier in contact with developing liquid in substantially constant spaced relation to the electrically conductive surface of an image intensifier for an extended period of time.

Another object of the present invention is to prevent scuff marks on the image-bearing carrier by poviding a developing path free from stationary ridges likely to accumulate a build-up of developer particles, and to eliminate relative movement between the image-bearing carrier and the surface which is used to transport the carrier past the image intensifying surface.

Still other objects, features and advantages of the present invention will be apparent to those skilled in the art from a reading of the following detailed description of the embodiments of the invention, taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a preferred embodiment of a developing station for developing a latent electrostatic image on the surface of a carrier into a visible image according to the present invention;

FIG. 2 is a plan view of the developing station shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along the lines 33 in FIG. 2, illustrating the developing path along which a latent image-bearing carrier is transported during movement past the developing station, wherein developing liquid is being applied to the surface of the image intensifying member prior to the passage of an image-bearing carrier along the developing path;

FIG. 4 is a view of the developing station as shown in FIG. 3, wherein an image-bearing carrier is being trans ported along the developing path and extending through the squeegee rollers;

FIG. 5 is a perspective view of another embodiment of a developing station constructed in accordance with the present invention;

FIG. 6 is a schematic view of still another embodiment of a developing station constructed in accordance with the present invention, and having an elongated distance of eifective field control spacing which is substantially linear.

Referring generally to FIGS. 1-4 in the drawings, there is shown a developing station, generally indicated 11, for developing a latent electrostatic image on a surface 1'3 of a carrier 15 into a visible image as the carrier 15 moves past the developing station 11 along a developing path. As the image-bearing carrier moves along the developing path, it is guided onto a moving transport belt 17 and brought into contact with developing liquid, generally indicated 19, which is pumped from a tank 21 through a header tube 23 onto the surface 25 of a rotating cylinder 27. The surface 25 of the cylinder 27 is electrically conductive and serves as an image intensifier to straighten out the lines of force of the electrostatic field produced by the latent electrostatic image. The transport belt 17 transports the image-bearing carrier 15 past the rotating cylinder 27 with the image-bearing surface 13 of the carrier 15 being maintained in substantially constant effective field control spacing with the surface 25 of the cylinder 27 over an elongated distance so as to enable the visible particles in the developing liquid 19 to be uniformly deposited on areas of the image having the same uniform electrostatic charge. From the transport belt 17, the image-bearing carrier 15 passes between the cooperating surfaces of a pair of rotating squeegee rollers, 29, 31 respectively, which remove excess developing liquid 19 from the carrier 15 and press the visible particles into the surface thereof to provide a permanent copy of an original document.

As shown, the image intensifying cylinder 27 is located between inboard and outboard side plates, 33, 35 respectively, and is mounted on a drive shaft 37 which is rotatably supported by the inboard and outboard side plates 33, 35. Beneath the image intensifying cylinder 27, the endless transport belt 17 extends limply around two parallel spaced rollers 39, 41 respectively, which are located on laterally opposite sides of the image intensifying cylinder 27. The endless transport belt 17 is maintained limp, or slack, so as to give the portion of the belt adjacent to the surface 25 of the image intensifying cylinder 27 a cross-sectional configuration which is substantially concentric with the surface 25 of the cylinder 27. Accordingly, the slackened belt 17 provides an elongated distance along the developing path in which the image-bearing surface 13 of the carrier 15 is in substantially constant spaced relation with the surface 25 of the cylinder 27.

The image intensifying cylinder 27 may be constructed from a suitable electrically conductive material, such as steel or aluminum. Alternatively, the cylinder may be formed from an electrically insulating material which is then coated with an electrically conductive material. The transport belt 17 may be constructed from an electrically insulating material, such as Mylar, and may be made endless by joining the ends together by suitable means, for example acoustical welding.

The roller 39 serves as a drive roller for moving the endless transport belt 17 along the developing path and is mounted on a drive shaft 43 which is rotatably supported by the inboard and outboard side plates 3-3, 35 respectively. To enable the drive roller 39 to move the slack endless transport belt 17, sprockets, generally indicated 45, are formed on the opposite ends of the drive roller 39 which engage spaced openings, generally indicated 47, formed in the endless transport belt 1'7 along the sides thereof. In addition, the surface of the drive roller 39 may be knurled to provide frictional engagement with the transport belt 17. The other roller 41 serves as an idler roller and is mounted on a shaft 49 having its opposite ends journaled in suitable inboard and outboard bearings 51, '53 respectively. As shown, the bearing 51 is supported by the inboard side plate 33 by means of a threaded bolt 52 which is inserted through a slot 54 formed in the side plate 33 and threaded into a threaded bore, not shown, which may be suitably formed in the bearing 51. The outboard bearing 53 is supported by the outboard side plate 35 in the same manner as the inboard bearing "51 is supported by the inboard side plate 33, and accordingly identical reference numerals have been placed on identical parts. The bolts 52 supporting the inboard and outboard bearings, 51, 53 respectively, are laterally movable in the slots formed in the side plates 33, 35 respectively, so as to vary the spacing between the rollers 39, 41 and hence the slack in the endless transport belt 17.

The inboard and outboard side plates 33, 35 respectively, are held together by spacer bars 55, 57 to form an image intensifying assembly which includes the image intensifying cylinder 27 and the endless transport belt 17. The spacer bars 55, 57 are located between the side plates 33, 35 on laterally opposite sides of the image intensifying cylinder 27, and may be connected to the side plates 33, 35 by suitable means. As shown, the spacer bar 55 has an axially extending reduced portion 59 which is threaded and forms an annular shoulder 61 for engaging the inboard side plate 33. The reduced threaded portion 59 extends through a suitable opening formed in the side plate 33 and has a threaded nut threaded thereon to hold the side plate 33 against the annular shoulder 61. The opposite end of the spacer bar 55 as Well as the ends of the spacer bar 57 have reduced threaded portions identical to the threaded portion 59, and the side plates 33, 35 are secured thereon in the same manner as previously described. Accordingly, identical reference numerals have been placed on identical portions.

The image intensifying assembly may be supported in a photocopying machine between two spaced side walls 65, 67 respectively, with a guide plate 69 located on one side, which will hereinafter be referred to as the input side, and with the squeegee rollers 29, 31 located on the other side, which will hereinafter be referred to as the output side. The guide plate 69 is suitably supported between the two spaced side walls 65, 67 respectively, for guiding an incoming image-bearing carrier 15 onto the transport belt 17 at the input side of the image intensifying assembly. The guide plate 69 is generally flat and inclined downwardly toward the transport belt 17 with the end 71 adjacent thereto being turned down to prevent an image-bearing carrier 15 moving along the guide plate 69 from contacting any developer particles which might accumulate on the end 71 of the guide plate 69.

As previously mentioned, the cooperating squeegee rollers 29, 31 which are located on the output side of the image intensifying assembly, remove excess developing liquid from the image-bearing carrier 15 and press the visible particles into the surface thereof. The cooperating squeegee rollers 29, 31 are rotatably supported between the two spaced side walls 65, 67 of the photocopying machine, with the roller '31 engaging the back side of the image-bearing carrier 15 while the roller 29 engages the image-bearing surface 13 thereof. The roller 31 is an idler roller having a sleeve 73 constructed from a resilient material, such as rubber, while the roller 29 is a drive roller which presses against the resilient sleeve 73 of the idler roller 31. The drive roller 29 is constructed from suitable electrically conductive material, such as steel, and may desirably be pressed against the idler roller 31 by conventional resilient biasing means, not shown.

The electrically conductive surface 25 of the image intensifying cylinder 27 and the electrically conductive squeegee roller 29 may both be electrically grounded by suitable means, for example through the hearings or through a brush contact, to the frame portions of the photocopying machine, for example the spaced side Walls 65, 67. In addition, the image intensifying cylinder 27, the drive roller 39 for the endless transport belt 17, and the squeegee roller 29 may all be separately driven by conventional drive means, not shown, or for that matter may be driven by a common drive means through a chain and sprocket arrangement.

Since the visible particles on the image-bearing surface 13 of the carrier 15 tend to adhere to the electrically conductive drive roller '29 as the carrier 15 passes between the squeege rollers 29, 31, a wiper, 75, is provided for Wiping the surface of the drive roller 29. As shown, the wiper 75 is constructed from a suitable porous material, such as open-celled polyurethane foam, and is held against the surface of the squeegee roller 29 by a suitable bracket 77 which is supported between the two spaced side walls 65, 67. As previously mentioned, a dry wiper oftentimes produces squeaking sounds and streaks the initial copies passing through the squeegee rollers 29, 31 until the wiper 75 becomes soaked with developing liquid so as to wipe the surface of the squeegee rollers 29 smoothly and uniformly. To avoid the undesirable results of a dry squeegee wiper 75, the wiper 75 extends into engagement with the surface 25 of the image intensifying cylinder 27 so as to absorb developing liquid from the moving surface thereof prior to the passage of an image-bearing carrier 15 through the squeegee rollers 29, 31. In addition, the wiper 75 serves to remove developer particles from the surface '25 of the image intensifying cylinder 27 which may accumulate during the development of a latent electrostatic image.

Beneath the image intensifying assembly is located the developing tank 21 containing the developing liquid 19 with the visible particles which are electrically attractable to the latent electrostatic image on the surface 13 of a carrier 15. The developing liquid is circulated from the tank 21 onto the surface 25 of the image intensifying cylinder 27 by a suitable pump 79 which is submerged in the developing liquid 19 and driven by a suitable motor 81. The pump 79 discharges the developing liquid 19 through a header tube 23 which extends across the surface 25 of the image intensifying cylinder 27 above the guide plate 69. The developing liquid 19 flows onto the moving surface 25 of the cylinder 27 through a series of spaced apertures formed in the header tube 23- which open toward the surface 25 of the cylinder 27. From the cylinder 27, the developing liquid 19 flows onto the endless transport belt 17 and forms a small pool, generally indicated at 83 at the nip of the cylinder 27 and the endless transport belt 17 and drains across the sides of the endless transport belt 17 onto a drain plate *85 covering the top of the tank 21. The drain plate 85 slopes downwardly towards an opening 87 formed in the center thereof through which the liquid drains back into the tank 21.

To prevent the developing liquid 19 from splashing over the sides of the tank 21 as it drains downwardly onto the drain plate 85, the tank 21 is provided with a rim 89 which extends along the upper edge of the tank 21. To enable the tank 21 to be easily removed from the photocopying machine for cleaning, the rim 89 at the end of the tank 21 opposite to that of the pump 79 has a recessed portion 91 formed therein through which the lower portion of the endless transport belt 17 may pass as the tank is removed from the photocopying machine. The recessed portion 91 of the rim 89 is covered by a strip 93 of suitably resilient material, such as rubber, and is held in place by a splash plate 95 which is fastened to the drain plate by suitable means, for example screws. The splash plate serves to entrap developing liquid moving toward the end of the tank 21 between the bottom side of the plate and the sloping surface of the drain plate 85, and thus prevent the liquid from splashing up over the strip 93 of resilient material.

When the operation of the photocopying machine is initiated in preparation for producing a copy of an original document, the image intensifying cylinder 27, the transport belt 17, and the squeegee rollers 29, 31 are driven and developing liquid 19 is circulated from the tank 21 through the header tube 23 onto the surface 25 of the image intensifying cllinder 27. Due to the slackness of the endless transport belt 17, the sprockets 45 of the drive roller 39 may slip past the spaced openings 47 in the transport belt 17 during initial rotation of the drive roller 39. To prevent this, suitable shoes 97 may be placed adjacent the ends of the drive roller 39 to hold the transport belt 17 onto the sprockets 45. In addition, if the photocopying machine has not been in use for a period of time, then a residue of developing liquid may cause the transport belt 17 to stick to the idler roller 41, and this may cause the seam of the endless transport belt 17 to split open when the drive roller 39 is initially driven. However, due to the rotatable mounting of the idler roller 41, the initial movement of the belt 17 rotates the idler roller 41 and enables the transport belt 17 to strip itself free from any residue of developing liquid holding it to the idler roller 41. When the transport belt 17 is brought up to the desired speed, which is substantially equal to the speed of an incoming imagebearing carrier 15, then the endless transport belt 17 no longer rotatably drives the idler roller 41 but instead slips over the surface thereof.

As developing liquid 19 is circulated from the tank 21 onto the surface 25 of the rotating image intensifying cylinder 27, it flows down the surface 25 of the cylinder 27 onto the transport belt 17 and drains across the sides thereof. From the transport belt 17 the developing liquid pours onto the drain plate 85 and flows across the downwardly sloping surface to the opening 87 formed therein where it drains back into the tank 21. If the photocopying machine has been inoperative for an extended period of time, then the wiper 75 engaging the squeegee roller 29 may have become dry and produce squeaking sounds and cause streaking of the initial copies moving past the squeegee rollers 29, 31. However, as more particularly shown in FIG. 3, the rotating image intensifying cylinder 27 moves developing liquid along the developing path and into contact with the wiper 75 which absorbs a portion of the developing liquid. As the cylinder 27 continues to rotate and bring more developing liquid into contact with the Wiper 75, the wiper 75 becomes soaked with developing liquid and the portion of the wiper 75 engaging the squeegee roller 29 becomes dampened so as to wipe the roller 29 smoothly and uniformly, thus eliminating squeaking sounds and avoiding streaks on the initial copies moving past the squeegee rollers 29, 3-1.

When an incoming image-bearing carrier 15 moves along the developing path, it is guided by the guide plate '69 onto the endless transport belt 17. As more particularly shown in FIG. 1, When the image-bearing carrier 15 moves into the nip of the image intensifying cylinder 27 and the endless transport belt 17, it causes the developing liquid 19 flowing down the surface 25 of the cylinder 27 to form a small pool which backs up on the image-bearing surface 13 of the carrier 15 and drains off along the sides thereof. As the endless transport belt 17 moves the image-bearing carrier 15 along the developing path, the image-bearing surface 13 of the carrier 15 is brought into the elongated distance of effective field control spacing with the image intensifying cylinder 27. It is believed that electrically conductive surface 25 of the cylinder 27 serves to straighten out the lines of force of the electrostatic field produced by the latent electrostatic image. As a result, the visible particles of the developing liquid confined in the effective field control space between the image-bearing surface 13 of the carrier 15 and the electrically conductive surface 25 of the image intensifying cylinder 27 are more uniformly de- 1 posited on areas of the latent electrostatic image the same uniform electrostatic charge.

It has been found that. the most effective field control having spacing for producing a copy having substantially Juniform deposition of visible developer particles on areas having substantially the same electrostatic charge extends from about 0.005 inch between the image-bearing surface 13 of the carrier15 and the electrically conductive surface 25 of the image intensifying cylinder 27. Moreover,

it has been found that a spacing of from about 0.005

tensifying cylinder 27 may be rotatably driven so that the surface 25 of the cylinder 27 moves along the developing path in the same direction as the image-bearing carrier 15 and with a speed substantially equal to that of the carrier .15. However, the quantity of visible'particles available to develop the latent electrostatic image may be in-' creased by rotatably driving the image intensifying cylinder 27 with a surface speed greater than that of the carrier 15, thus bringing a greater quantity of developing liquid into contact with the carrier 15 as it moves through the elongated distance of effective field control spacing. Alternatively, the image intensifying cylinder 27 may be rotatably driven in a direction opposite to the movement of the carrier 15 to bring unused visible particles into proximity with undeveloped portions of the latent image on the carrier 15. However, such reverse rotation of the cylinder 27 will tend to diminish the space-between the surface of the cylinder 27 and the image-bearing surface 13 of the carrier 15, thus reducing the quantity of developing liquid available to develop the latent image.

From the image intensifying cylinder 27, the-endless transport belt 17 moves the image-bearing carrier 15 into the nip of the cooperating squeegee rollers 29, 31.which are being rotatably driven. The roller 29 engages the image-bearing surface 13 of the carrier 15 and presses it against the resilient sleeve 73 of the roller 31 so as to remove excess developing liquid 19 from the carrier 15 and press the visible particles into the surface thereof. The squeegee rollers 29, 31 are rotatably driven so that the peripheral speed of the cooperating surfaces is substantially equal to the linear speed of the image-bearing carrier 15. Accordingly, the carrier 15 is removed from the endless transport belt '17 without any resulting differential speed being produced which may bring the imagebearing surface 13 of the carrier 15 into contact with the rotating image intensifying cylinder 27 and thus cause the developed image to become smeared.

Another embodiment of a developing station constructed in accordance with the present invention is shown diagrammatically in FIG. 5. With the exception of the image intensifying assembly, the developing station, gen

erally indicated 11', of this embodiment is generally identical to the developing station 11 described in'the previous embodiment, and accordingly identical reference numerals have been placed on identical portions thereof. In this,

embodiment, the image intensifying cylinder 27 has axially spaced annular flanges 99, 101 engaging the endless trans- -s port belt 17 so as to maintain the transport belt 17 in spaced relation to the electrically conductive surface 25 of the image intensifying cylinder 27.

As in the previous embodiment, the endless transport belt 17 extends around two rollers 39, 41 which are spaced apart and rotatably supported. In this embodiment however, the rollers 39, 41 are sufiiciently spaced apart to 'maintain the endless transport belt 17 ina taut condition and pressed against the annular flanges 99, 101 of the image intensifying cylinder 27. Although not' shown, the tautness'of the'belt 17'may desirably be maintained substantially constant by providing suitable resilient biasing means urging the spaced rollers 39, 41 apart from each other. Furthermore, since the endless transport belt 17 is being maintained in a taut condition as opposed to the slack condition illustrated in the previous embodiment, the drive roller 39 need not be provided with sprockets, but instead may drive the endless transport belt117 by means of friction. Although not shown, a wiper may be provided for wiping the surface of the squeegee roller 29, and the wiper mayextend into engagement with the moving surface 25 of the image intensifying cylinder 27,,as-described in the previous embodiment, so as to become soaked with developing liquid and thuseliminate squeaking sounds and streaking. of copies passing between the squeegeerollers 29, 31 respectively.

In operation, developing liquid-19, is applied to the electrically conductive surface 25 of the image intensifying cylinder 27, and the cylinder 27 is rotatably driven to bring the developing liquid 19 into the elongated distance of effective field control spacing between the surface 25 of the cylinder 27 and the surface of the endless transport belt 17. An incoming, image-bearing carrier moving along the developing path is guided by the guide plate onto the endless transport belt 17 between the axially spaced annular flanges 99, 101 of the image intensifying cylinder 27. The annular flanges 99, 101 extend radially from the surface 25 of the cylinder '27 a distance sufiicient to enable the carrier 15 to be moved along the developing path with the image-bearing surface 13 thereof in substantially constant effective field control spacing with the electrically conductive surface 25 of the image intensifier 27.

Still another embodiment of a developing station constructed in accordance with the present invention is shown in FIG. 6. With the exception of the image intensifying assembly, the developing station, generally indicated 11" of this embodiment is generally identical to that described in connection with FIGS. 1-4, and accordingly identical reference numerals have been placed on identical portions thereof. In this embodiment, the image intensifyingmeans is in the form of an endless belt 103 having an electrically conductive surfacei 105 which is movable along the developing path. The image intensifying 'belt 103 extends around two rotatably supported rollers 107, 109 which are spaced sufficiently apart to maintain the image intensifying belt 103 in a taut condition. Beneath the image intensifying belt 103 is mounted the endless transport belt 17 which moves along the developing path substantially parallel with the adjacent surface 105 of the image intensifying belt 107. The endless transport belt '17 also extends around two rotatably supported rollers 39, 41 which are spaced sufficiently apart to maintain the endless transport belt 17 in a taut condition. Due to the taut conthe image intensifying belt 103 for receiving the incoming image-bearing carrier 15 as it moves along the developing path. On the output side of the image intensifying assembly, the cooperating squeegee rollers 29, 31 are located with the nip of the rollers 29, 31 lying in the plane defined by the adjacent surfaces of the image intensifying belt 103 and the endless transport belt 17 so as to receive the image-bearing carrier as it is transported past the elongated distance of effective field control spacing. Although not shown, a wiper may be provided for wiping the surface of the squeegee roller 29, and the Wiper may extend into engagement with the moving surface 105 of the image intensifying belt 103 in the same manner previously described so as to enable the wiper to become soaked with developing liquid and thus Wipe the surface of the squeegee roller 29 smoothly and uniformly.

In operation, an incoming image-bearing carrier 15 is guided by the guide plate 69 onto the endless transport belt 17 where it comes into contact with developing liquid 19 being applied through a header tube 23 onto the surface of the image intensifying belt 105. The endless transport belt 17 moves the image-bearing carrier 15 along the developing path into the elongated distance of elfective field control spacing provided by the electrically conductive surface 105 of the image intensifying belt 103' which is moving parallel with the endless transport belt 17. Accordingly, the lines of force of the electrostatic field produced by the latent electrostatic image are straightened so as to provide uniform deposition of visible particles on the image-bearing surface 13 of the carrier 15 as it moves along the developing path.

From the image intensifying assembly, the image-bear ing carrier 15 moves into the nip of the rotatably driven squeegee rollers 29, 31 which remove excess developing liquid from the carrier 15 and press the visible particles into the surface thereof to provide a permanent copy of the original document. Although the nip of the rotating squeegee rollers 39, 41 is shown as lying in the same plane as the elongated distance of effective field control spacing, they may be located above or below the plane and a suitable guide may be placed on the output side of the image intensifying assembly to guide the image-bearing carrier into the nip of the rollers.

While only a limited number of embodiments have been illustrated and described, it will be apparent to those skilled in the arts that various modifications and improvements may be made without departing from the scope and spirit of the invention. Accordingly, it is to be understood that the invention is not to be limited by the illustrative embodiments, but only by the scope of the appended claims.

What is claimed'is:

' 1. A method of developing a latent electrostatic image on a surface of a carrier, comprising the steps of wetting an electrically conductive surface with an electrophotographic developing liquid, moving the electrically conductive surface along a developing path, moving an imagebearing surface of a carrier into engagement with the electrophotographic developing liquid on the moving electrically conductive surface, and transporting the image bearing carrier along the developing path with the imagebearing surface being in contact with the electrophotographic developing liquid and in substantially constant spaced relation from the moving electrically conductive surface over an elongated distance in substantially the direction of movement of the carrier, to increase the period of time the image-bearing carrier is in substantially constant spaced relation from the moving electrically conductive surface.

2. A method of developing a latent electrostatic image on a surface of a carrier according to claim 1, wherein the electrically conductive surface is moved along the developing path in the same direction as the image-bearing carrier is transported along the developing path, and the imagebearing carrier is transported along the developing path at a speed substantially equal to the speed of the moving electrically conductive surface.

3. A method of developing a latent electrostatic image on a surface of a carrier according to claim 1, wherein said electrically conductive surface moves along the developing path in the same direction and at substantially the same speed as the image-bearing carrier moves along the developing path, and comprising the additional steps of moving cooperating squeegeeing surfaces into contact with each other for receiving the image-bearing carrier, said cooperating squeeging surface moving at substantially the same speed as the image-bearing carrier moves along the developing path, and moving the imagebearing carrier between the moving cooperating squeegeeing surfaces for removing excess liquid from the carrier.

4. A method of developing a latent electrostatic image on a surface of a carrier which comprises mounting an image intensifying member with an electrically conductive surface for movement along a developing path, mounting an endless belt beneath said image intensifying member for movement along the developing path with the surface thereof in substantially constant spaced relation to the surface of the image intensifying member throughout an elongated distance to provide an elongated distance of effective field control spacing for an image-bearing surface of a carrier moving along the developing path on the surface of the endless transport belt, applying a developing liquid containing particles electrically attractable to areas on the image-bearing surface of the carrier to the electrically conductive surface of the image intensifying member, moving the image intensifying member along the developing path so as to bring the developing liquid into the elongated distance of effective field control space, moving a carrier with a latent electrostatic image along the developing path onto the surface of the endless transport belt with the image-bearing surface facing the surface of said image intensifying member, and moving the endless transport belt to bring the image-bearing surface of the carrier into contact with the developing liquid and move the carrier past the elongated distance of effective field control spacing provided by the electrically conductive surface of the image intensifying member to increase the period of time the said surface of the carrier is in effective field control spacing with the image intensifying member.

5. A method of developing a latent electrostatic image on a surface of a carrier according to claim 4, wherein the surface of the endless transport belt, is moved along the developing path past the electrically conductive surface of the image intensifying member at a speed substantially equal to the speed of the image-bearing carrier moving onto the endless transport belt.

6. A'method of developing a latent electrostatic image on a surface of a carrier according to claim 5, wherein the electrically conductive surface of the image intensifyingrnember is moved in the same direction along the developing path as the image-bearing carrier.

7. A method of developing a latent electrostatic image on a surface of a carrier according to claim 6, which further comprises mounting a pair of squeegee members having cooperating surfaces for movement into engagement with each other on the developing path, moving the squeegee members to bring the cooperating surfaces thereof into engagement with each other on the developing path for receiving the image-bearing carrier, said cooperating squeegeeing surfaces being moved at substantially the same speed as the image-bearing carrier moves past the elongated distance of effective field control spacing, and moving the image-bearing carrier between the cooperating surfaces of the squeegee members for removing excess liquid from the carrier.

8. Apparatus for developing a latent electrostatic image on a surface of a carrier into a visible image, comprising intensifying means having an electrically conductive surface movable along a developing path, transport means for moving a carrier with a latent electrostatic image along said developing path, said transport means being an endless belt and having a surface thereof movable along said developing path over an elongated distance in substantially constant spaced relation from the surface of said image intensifying means to provide an elongated distance of effective field control spacing for an imagebearing carrier being transported along said developing path, fluid supply means for applying fluid to the surface of said image intensifying means, and drive means for simultaneously moving the surface of said image intensifying means and the surface of said transport means along said developing path, whereby the carrier with the latent electrostatic image is brought into contact with the developing fluid and transported along said developing path past an elongated distance of effective field control spacing to increase the period of time the carrier with the latent electrostatic image is in effective field control spacing with the surface of said image intensifying means.

9. Apparatus according to claim 8, wherein said electrically conductive surface of said image intensifying means moves along said developing path in a substantially straight plane, and the surface portion of said transport means moves along said developing path substantially parallel to the surface of said image intensifying means so as to provide a developing path having a substantially straight planar area of effective field control spacing.

10. Apparatus according to claim 9, wherein said image intensifying means comprises an endless belt having an electrically conductive surface facing the image-bearing surface of a carrier moving along said developing path, and means for mounting said image intensifying belt for movement in a substantially straight line along said developing path.

11. Apparatus according to claim 10, wherein said transport means includes an endless belt having a substantially electrically insulating surface, and means for mounting said transport belt for movement along said developing path substantially parallel to said image intensifying belt.

12. Apparatus according to claim 8, wherein said electrically conductive surface of said image intensifying means has an arcuate cross-sectional configuration and moves along said developing path in an arcuate direction, and said surface portion of said transport means moves along said developing path substantially parallel to the surface of said image intensifying means so as to provide a developing path having an elongated distance of effective field control spacing.

13. Apparatus according to claim 12, wherein said image intensifying means includes a cylinder having an electrically conductive surface, said cylinder being rotatably mounted for movement about its axis and having axially spaced annular flanges, said transport means includes an endless belt having an electrically insulating surface, and said transport means further includes means for mounting said endless transport belt in engagement with said axially spaced annular flanges for movement about a portion of said image intensifying cylinder, whereby a portion of the outer surface of said endless transport belt is substantially concentric with the surface of said image intensifying cylinder.

14. Apparatus according to claim 13, wherein said means for mounting said endless transport belt includes first and second cylindrical guide means mounted beneath said image intensifying cylinder and on opposite sides thereof with their axes parallel withv the axis of said cylinder, said endless transport belt being movable over said cylindrical guide means, and said first and second cylindrical guide means being spaced apart to place said endless transport belt under tension and press it into engagement with said annular flanges of said image intensifying cylinder.

15. Apparatus for developing a latent electrostatic image on a surface of a carrier into a visible image according to claim 12, wherein said image intensifying means is a cylinder having an electrically conductive surface and being rotatably mounted for movement about its axis, said transport means inclduing an endless belt mounted beneath said image intensifying cylinder for movement along said developing path, said transport means further including two spaced cylindrical guide means mounted beneath said image intensifying cylinder and having their axes parallel with the axis of said cylinder, said endless belt being slackened and having a cross-sectional surface configuration adjacent to the surface of said image intensifying cylinder which is substantially concentric therewith to provide an elongated distance of effective field con trol spacing along said developing path, whereby an image-bearing carrier moving along said developing path is transported past the electrically conductive surface of said image intensifying cylinder through an elongated distance of effective field spacing.

16. Apparatus for developing a latent electrostatic image on a surface of a carrier according to claim 15, wherein one of said cylindrical guide means supporting said endless belt for movement along said developing path is a cylindrical roller, said endless transport belt having spaced apertures formed therein along the edges, and said cylindrical roller having sprockets formed thereon for engaging said spaced apertures formed in said endless belt for moving said slack endless belt along said developing path.

References Cited UNITED STATES PATENTS 1,275,216 8/1918 Cady 118-429 X 1,653,610 12/1927 Aitchison 118-426 X 1,846,201 2/1932 Hoffmeister 118-426 X 2,128,028 8/1938 Hampton 118-429 X 2,877,739 3/ 1959 Payne 118-429 X 3,203,395 8/ 1965 Liller 118-637 3,249,088 5/ 1966 Ostensen 118-637 3,345,925 10/ 1967 Ostensen 118-637 X 3,347,691 10/ 1967 Lyles 118-637 X 3,367,791 2/1968 Lein 117-37 3,368,526 2/ 1968 Matsumoto et al. 118-429 X 3,377,988 4/1968 Zawiski 117-37 X 3,472,657 10/ 1969 Mayer et al 118-637 X 3,169,887 2/1965 York 117-37 X WILLIAM D. MARTIN, Primary Examiner M. SOFOCLOUS, Assistant Examiner US. Cl. X.R.

1l8Digest 23, 637; 355-10 

